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INA828: CMV vs Output voltage in single supply / 0 Vdc Vref low gain configuration.

Doug Robertson
Prodigy 10 points
Part Number: INA828
Other Parts Discussed in Thread: INA823, TINA-TI

Tool/software:

Operating this INA828 as follows:

+Vs = 19.75 Vdc

-Vs = 0 Vdc

Vref = 0 Vdc

Gain = 3.6

-In = 2.554 Vdc

+In = 3.943 Vdc

TI calculator says I should be able to reach greater than 5.0 Vdc at output but I actually can only get about 4.6Vdc max.  At a 1/2 full-scale differential input (.695 Vdc) I get 2.50 Vdc at the output as expected, but it won't go to 5.0 Vdc for the full differential input of 1.39 Vdc.  Have tried multiple devices.  Any ideas?  Looks Like a INA823 might work, but just trying to figure out why the INA828 does not.

  • 0
    TI__Mastermind 33723 points

    Hey Doug,

    One of the ways we can hint at what's going on is by probing the voltage on either side of RG relative to ground. Pin 8 corresponds to the IN+ amplifier, Pin 1 corresponds to the IN- amplifier. When your output is nonlinear, RG Pin 8 should be the same voltage as IN+, and RG Pin 1 should be the same voltage as IN-. If this is not the case, you can see if A1 or A2 are outside of linear operating range.

    Throwing this in a quick TINA-TI sim I suspect that it would be the IN- amplifier, as it is closest to the rail, but I would suspect that the internal amplifier should be able to swing ~750mV from V- linearly.

    Is there any output load resistance connected to the device?

    Are you able to share a schematic?

    Best,
    Gerasimos